Liquid crystal composition and display element using the same

ABSTRACT

##STR1## A liquid crystal composition and a display element using the same are disclosed. The composition contains at least one dichroic dye represented by general formula (I), at least one dichroic dye represented by general formula (II), and at least one dichroic dye represented by general formula (III). In formula (I), R1 to R3 each represent a hydrogen atom, an alkyl group, an optionally substituted cycloalkyl group, an alkoxyalkyl group, an alkoxy group or a halogen atom; and A represents (a); in formula (II), R4 and R5 each represents a hydrogen atom, an alkyl group, an optionally substituted cycloalkyl group, an alkoxyalkyl group, an alkoxy group or a halogen atom; in formula (III), R6 represents a hydrogen atom, an alkyl group, an optionally substituted cycloalkyl group, an alkoxyalkyl group, an alkoxy group or a halogen atom. R7 represents a hydrogen atom or (b), and R8 represents a hydrogen atom, an alkyl group, an optionally substituted cycloalkyl group, an alkoxyalkyl, an alkoxy group or a halogen atom.

FIELD OF THE INVENTION

This invention relates to a liquid crystal composition, which isexcellent in stability at a low temperature, contrast andlight-resistance and a display element using the same.

BACKGROUND OF THE INVENTION

A display element taking advantage of a guest/host effect achieved byadding a dichroic dye to liquid crystals has attracted public attentionas a display element suitable for a medium to large-scale display, sinceit has the following advantages:

(1) Having a wide angle of view;

(2) Capable of readily realizing a colorful display by selecting dyes;and

(3) Not always requiring a polarizing plate and thus capable of giving aclear display.

Conventional display elements taking advantage of a guest/host effectachieved by adding a dichroic dye to liquid crystals can hardly satisfya high stability at a low temperature, a high contrast, highlightshielding properties, a long lifetime and various hues at the sametime. A contrast ratio is expressed in the ratio of the volume of lightat the transmission to that at the shade. In order to achieve a highcontrast ratio, therefore, it is required not only to give a highdichroic ratio of the dye but also to lower the volume of transmittedlight corresponding to the denominator, namely, elevating the solubilityof the dichroic dye. When different types of dyes are blended together,however, an irregularity is sometimes observed in the solubility of eachdye component in the blending system and that observed when each dye isused alone. That is to say, the solubilities in the blending systemfrequently fail to achieve an additive property. When different types ofdyes are blended together, furthermore, the photo-deterioration of someof these dyes is frequently accelerated. As a result, it becomesdifficult to simultaneoulsy satisfy a high stability at a lowtemperature, a high contrast, high light insulating properties and along lifetime in the cases of, in particular, practically valuablecolors such as black or dark blue.

In order to overcome these problems, JP-A-62-064887 has disclosed aliquid crystal composition comprising specific dichroic dyes of threetypes and a display element using the same.

It is an object of the present invention to provide a color liquidcrystal composition which is excellent in stability at a lowtemperature, contrast and light-resistance and superior, in particular,in contrast and light-shieding properties to the one disclosed inJP-A-62-064887 as well as a display element to thereby solve theabovementioned problems such as the irregularity in solubilities andphotodeterioration.

DESCRIPTION OF THE INVENTION

The gist of the present invention resides in a liquid crystalcomposition comprising at least one dichroic dye represented by each ofthe following general formulae I to III and in a display element usingsaid composition. ##STR2## wherein R¹ to R³ represent each a hydrogenatom, an alkyl, an optionally substituted cycloalkyl, an alkoxyalkyl oran alkoxy group or a halogen atom; and A represents a ##STR3## group.##STR4## wherein R⁴ and R⁵ represent each a hydrogen atom, an alkyl, anoptionally substituted cycloalkyl, an alkoxy-alkyl or an alkoxy group ora halogen atom. ##STR5## wherein R⁶ represents a hydrogen atom, analkyl, an optionally substituted cycloalkyl, an alkoxyalkyl or an alkoxygroup or a halogen atom; and R⁷ represents a hydrogen atom or a ##STR6##group; wherein R⁸ represents a hydrogen atom, an alkyl, an optionallysubstituted cycloalkyl, an alkoxyalkyl or an alkoxy group or a halogenatom.

Now the present invention will be described in detail. Examples of thegroups R¹ to R⁶ and R⁸ include a hydrogen atom; straight-chain orbranched alkyl groups such as methyl, ethyl, propyl, butyl, pentyl,hexyl, octyl, nonyl and dodecyl groups; cycloalkyl groups optionallysubstituted with, for example, straight-chain or branched alkyl group(s)such as propylcyclohexyl, butylcyclohexyl, pentylcyclohexyl,hexylcyclohexyl and octylcyclohexyl groups; straight-chain or branchedalkoxyalkyl groups such as methoxymethyl, butoxymethyl, ethoxyethyl andbutoxyethyl groups; straight-chain or branched alkoxy groups such asmethoxy, ethoxy, propoxy, butoxy, pentoxy and octoxy groups; and halogenatoms such as fluorine, chlorine and bromine atoms.

In the dye represented by the general formula I, it is preferable thatR¹ and R³ represent each a hydrogen atom or an alkyl group; R²represents a hydrogen atom; and A represents a ##STR7## group.

It is further preferable that R¹ represents a hydrogen atom or an alkylgroup having 1 to 8 carbon atoms and R³ represents an alkyl group having1 to 8 carbon atoms. It is the most preferable that R¹ and R²

represent each a hydrogen atom; R³ represents an alkyl group having 1 to8 carbon atoms; and A represents a ##STR8## group.

In the dye represented by the general formula II, it is preferable thatR⁴ and R⁵ represent each a hydrogen atom or an alkyl group.

It is further preferable that R⁴ and R⁵ represent each an alkyl grouphaving 2 to 8 carbon atoms.

In the dye represented by the general formula III, it is preferable thatR⁶ represents a hydrogen atom or an alkyl group; R⁷ represents ahydrogen atom or a ##STR9## group; and R⁸ represents a hydrogen atom oran alkyl group.

It is further preferable that R⁶ represents an alkyl group having 2 to10 carbon atoms; R⁷ represents a hydrogen atom or a ##STR10## group; andR⁸ represents an alkyl group having 2 to 8 carbon atoms.

Examples of dyes available in the present invention are summarized inthe following Table 1. However it is needless to say that the presentinvention is not restricted thereby.

                                      TABLE 1                                     __________________________________________________________________________                                      Dye                                             General formula                   R.sup.1                                                                              R.sup.2                                                                          R.sup.3                                                                             A                       __________________________________________________________________________         ##STR11##                    I-1 H      H  C.sub.4 H.sub.9 (N)                                                                  ##STR12##                                                I-2 CH.sub.3                                                                             H  C.sub.2 H.sub.5                                                                      ##STR13##                                                I-3 C.sub.4 H.sub.9 (t)                                                                  H  C.sub.4 H.sub.9 (n)                                                                  ##STR14##                                                I-4 C.sub.4 H.sub.9 (t)                                                                  H  C.sub.6 H.sub.13 (n)                                                                 ##STR15##                                                I-5 C.sub.4 H.sub.9 (n)                                                                  H  C.sub.4 H.sub.9 (n)                                                                  ##STR16##                                                I-6 C.sub.6 H.sub.13 (t)                                                                 H  C.sub.6 H.sub.13 (n)                                                                 ##STR17##                                                I-7 C.sub.4 H.sub.9 (n)                                                                  H  C.sub.4 H.sub.9 (n)                                                                  ##STR18##                                                I-8 C.sub.4 H.sub.9 (n)                                                                  H  C.sub.6 H.sub.13 (n)                                                                 ##STR19##              I                                                                                  ##STR20##                    I-9 C.sub.6 H.sub.13 (n)                                                                 H  C.sub.4 H.sub.9 (t)                                                                  ##STR21##                                                I-10                                                                              C.sub.2 H.sub.5                                                                      H  C.sub.6 H.sub.13 (n)                                                                 ##STR22##                                                I-11                                                                              C.sub.3 H.sub.7 (n)                                                                  H  C.sub.5 H.sub.11 (n)                                                                 ##STR23##                                                I-12                                                                              H      H  C.sub.4 H.sub.9 (n)                                                                  ##STR24##                                                I-13                                                                              H      H  CH.sub.3                                                                             ##STR25##                                                I-14                                                                              H      H  C.sub.3 H.sub.7 (n)                                                                  ##STR26##              __________________________________________________________________________                                            Dye                                      General formula                          R.sup.4                                                                             R.sup.5                     __________________________________________________________________________    II                                                                                ##STR27##                           II-1 II-2 II-3                                                                    C.sub.4 H.sub.9 (n) C.sub.4                                                   H.sub.9 (n) H                                                                       C.sub.4 H.sub.9 (n)                                                           C.sub.7 H.sub.15 (n)        __________________________________________________________________________                                                      H                                                                   Dye                                      General formula                          R.sup.6                                                                             R.sup.7                     __________________________________________________________________________    III                                                                               ##STR28##                           III-1 III-2 III-3                                                                 C.sub.4 H.sub.9 (n)  C.sub.8                                                  H.sub.17 (n)  C.sub.6                                                         H.sub.13 (n)                                                                        H H H                                                               III-4                                                                             C.sub.4 H.sub.9 (n)                                                                  ##STR29##                                                          III-5                                                                             C.sub.4 H.sub.9 (n)                                                                  ##STR30##                                                          III-6                                                                             H     H                           __________________________________________________________________________

In the present invention, it is required to use at least one of each dyerepresented by the formula I, II and III. It is further preferable thateach of the dyes of these three types is selected from among thepreferable ones described above.

Furthermore, it is preferable to use two or more dyes represented by thegeneral formula III.

In the above case, it is still preferable to use in combination of atleast one dye of the general formula III wherein R⁷ is a hydrogen atomand at least one wherein R⁷ is a ##STR31## group.

Furthermore, it is preferable that cyclohexyl groups in the generalformulae I, II and III are each a trans-cyclohexyl group.

Examples of the liquid crystals to be used in the present inventioninclude those represented by the following general formulae: ##STR32##wherein R⁹ and R¹⁰ represent each an alkyl, an alkoxyalkyl, an alkoxy,and alkylphenyl, an alkoxyalkylphenyl, an alkoxyphenyl, analkylcyclohexyl, an alkoxyalkylcyclohexyl, an alkylcyclohexylphenyl, acyanophenyl, a cyano group, a halogen atom, an alkoxycarbonyl, analkoxyalkoxycarbonyl, an alkylphenoxycarbonyl, analkoxyalkylphenoxycarbonyl, an alkoxyphenoxycarbonyl, analkylcyclohexyloxycarbonyl, an alkoxycyclohexyloxycarbonyl, analkylcyclohexylphenoxycarbonyl, a cyanophenoxycarbonyl, ahalogenphenoxycarbonyl, an alkylphenylalkyl, an alkoxyalkylphenylalkyl,an alkoxyphenylalkyl, an alkylcyclohexylalkyl, analkoxyalkoxycyclohexylalkyl, an alkylcyclohexylphenylalkyl or acyanophenylalkyl group, wherein an alkyl or an alkoxy chain mayoptionally have an optical active center and a phenyl or a phenoxy groupin the R⁹ or R¹⁰ group may be optionally substituted with a halogen atomsuch as a fluorine or a chlorine atom; and X represents a hydrogen atomor a halogen atom such as a fluorine or chlorine atom; and mixturesthereof.

Preferable examples thereof are nematic liquid crystal mixtures mainlycomprising a phenylcyclohexane liquid crystal compound.

The abovementioned liquid crystal mixture may further contain variousadditives such as an optically active material such as cholesterylnonanoate, an UV absorber or an antioxidant.

The liquid crystal composition of the present invention may be readilyprepared by dissolving the dyes represented by the above formulae I, IIand III in the abovementioned liquid crystal material.

The liquid crystal composition thus obtained is inserted intoelectrodes, at least one of which is transparent, to thereby form adisplay element by taking advantage of the guest/host effect.

The abovementioned display element may be constructed according to amethod described in, for example, "Ekisho no Saishin Gijutsu" [S.Matsumoto and I. Tsunoda, Kogyo Chosakai, 34 (1983) or J.L. FergasonSID85 Digest, 68 (1985)].

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

To further illustrate the present invention, and not by way oflimitation, the following Examples will be given.

In the following Examples, the dichroic properties are evaluated by theorder parameter (S) of each dye compound calculated according to thefollowing equation:

    (S)=(A// -A⊥)/(2A⊥+A//)

wherein A// and A⊥ represent the absorbances of the dye against lightsparallelly and vertically polarized to the direction of the alignment ofthe liquid crystals respectively.

More particularly, the order parameter (S) indicates the displaycontrast of a guest/host type liquid crystal display element. As thisvalue theoretically aproaches 1, the degree of the residual colorationin a white part is lowered, which enables a clear display of a highcontrast ratio.

The number of each dye used in the following Examples corresponds tothose specified in Table 1.

Example 1

The following dichroic dyes were dissolved in 100 g of a liquid crystalmixture mainly comprising phenylcyclohexane compounds (ZLI-1565 mfd. byE. MERCK Co.) to thereby prepare a liquid crystal composition 1.

Dye

I-1 4.13 g

II-1 2.76g

III-1 1.20 g and

III-4 2.00 g.

Next, the liquid crystal composition thus obtained was charged into acell having 9 μm gap and consisting of a glass plates providedtransparent electrodes, on which a polyimide resin had been applied andhardened followed by being homogeneously aligning by rubbing, positionedin such a manner that said liquid crystal display element was obtained.

The order parameters (S) of this liquid crystal display element at 637,575, 535 and 469 nm were 0.74, 0.76, 0.75 and 0.78 respectively, whilethe absorbances (A//) to the light parallelly polarized to the directionof the alignment were 1.470, 1.912, 1.590 and 1.770 respectively. Theliquid crystal composition 1 and the cell containing the same wereallowed to stand at -20° C. for 1000 hours. As a result, no abnormalitysuch as the precipitation of the dyes was observed. The light-resistanceof the cell containing the liquid crystal composition 1 was rested byusing a Fade-Ometer (carbon arc light source). As a result, the huechange (.increment.E) after 100 hours (determined by L*a*b* method) wasnot more than 1.5 while the current gain (I/Io; applied voltage: 5 V, 32Hz) was 5.5.

Example 2

The procedure of Example 1 was repeated except that the followingdichroic dyes were used to thereby give a liquid crystal composition.

Dye

I-3 4.20 g

II-1 2.76 g

III-1 1.20 g and

III-4 2.00 g.

Next, a display element was formed by using the above liquid crystalcomposition. The order parameters of this liquid crystal display elementat 637, 575, 535 and 469 nm were 0.74, 0.76, 0.75 and 0.78 respectively,while the absorbances (A//) to the light parallelly polarized to thedirection of the alignment were 1.470, 1.912, 1.590 and 1.770respectively. The liquid crystal composition and the cell containing thesame were allowed to stand at -20° C. for 1000 hours. As a result, theliquid crystal composition remained stable. The light-resistance of thecell was tested in the same manner as the one described in Example 1.Then it showed a .increment.E value (L*a*b* method) of not more than 1.5and a current gain (I/Io) of 5.5.

Example 3

The procedure of Example 1 was repeated except that the followingdichroic dyes were used to thereby give a liquid crystal composition II.

Dye

I-4 2.30 g

I-5 2.15 g

II-1 2.76 g

III-1 1.20 g

III-4 1.00 g and

III-5 1.20 g.

Next, a display element was formed by using the above liquid crystalcomposition II. The order parameters(s) of this liquid crystal displayelement at 636, 575, 533 and 468 nm were 0.74, 0.76, 0.75 and 0.79respectively, while the absorbances (A//) to the light parallellypolarized to the direction of the alignment were 1.480, 1.910, 1.595 and1.780 respectively. The liquid crystal composition II and the cellcontaining the same were allowed to stand at -20° C. for 1000 hours. Asa result, no abnormality such as the precipitation of the dyes wasobserved. The light-resistance of the cell containing the liquid crystalcomposition II was tested by using a Fade-Ometer (carbon arc lightsource). As a result, the hue change (.increment.E) after 100 hours(L*a*b* method) was not more than 1.5 and a current gain (I/Io; appliedvoltage: 5 V, 32 Hz) of 5.2.

Example 4

The following dichroic dyes were dissolved in 100 g of a liquid crystalmixture mainly comprising phenylcyclohexane compounds (ZLI-1840 mfd. byE. MERCK Co.) to thereby prepare a liquid crystal composition III.

Dye

I-6 3.45 g

I-7 3.23 g

II-1 4.10 g

III-1 0.90 g

III-2 1.02 g

III-4 1.65 g and

III-5 1.88 g.

Next, the liquid crystal composition thus obtained was charged into acell having 9 μm gap and consisting of a glass plates provided withtransparent electrodes, on which a polyimide resin had been applied andhardened followed by being homogeneously aligning by rubbing, positionedin such a manner that said aligned surfaces were faced to each other.Thus a liquid crystal display element was obtained.

The order parameters (S) of this liquid crystal display element at 635,580, 535 and 470 nm were 0.74, 0.76, 0.75 and 0.77 respectively, whilethe absorbances (A//) to the light parallelly polarized to the directionof the alignment were 2.230, 2.860, 2.400 and 2.670 respectively. Theliquid crystal composition III and the cell containing the same wereallowed to stand at -20° C. for 1000 hours. As a result, no abnormalitysuch as the precipitation of the dyes was observed. The light-resistanceof the cell containing the liquid crystal composition III was tested byusing a Fade-Ometer (carbon arc light source). As a result, the huechange (.increment.E) after 100 hours (determined by L*a*b* method) wasnot more than 1.7 while the current gain (I/Io; applied voltage: 5 V, 32Hz) was 5.9.

Example 5

The following dichroic dyes were dissolved in 100 g of a liquid crystalmixture mainly comprising phenylcyclohexane compounds (9160; mfd. byChisso K.K.) to thereby prepare a liquid crystal composition IV.

Dye

I-5 1.40 g

I-8 1.30 g

I-9 1.55 g

II-1 1.40 g

II-2 1.48 g

III-1 0.49 g

III-2 0.52 g

III-3 0.25 g

III-4 1.10 g and

III-5 1.25 g.

Next, the liquid crystal composition thus obtained was charged into acell having 9 μm gap and consisting of glass plates provided withtransparent electrodes, on which a polyimide resin had been applied andhardened followed by being homogeneously aligning by rubbing, positionedin such a manner that said aligned surfaces were faced to each other.Thus a liquid crystal display element was obtained.

The order parameters (S) of this liquid crystal display element at 635,577, 535 and 466 nm were 0.75, 0.76, 0.75 and 0.79 respectively, whilethe absorbances (A//) to the light parallelly polarized to the directionof the alignment were 1.520, 1.970, 1.615 and 1.820 respectively. Theliquid crystal composition IV and the cell containing the same wereallowed to stand at -20° C. for 1000 hours. As a result, no abnormalitysuch as the precipitation of the dyes was observed.

The light-resistance of the cell containing the liquid crystalcomposition IV was tested by using a Fade-Ometer (carbon arc lightsource). As a result, the hue change (.increment.E) after 100 hours(determined by L*a*b* method) was not more than 1.3 while the currentgain (I/Io; applied voltage: 5 V, 32 Hz) was 5.2.

POSSIBILITY FOR UTILIZING IN INDUSTRY

The present invention provides a liquid crystal composition whereinspecific dichroic dyes are combined and a guest/host effect is utilizedas well as a display element employing the same. This liquid crystalcomposition is excellent in stability at a low temperature, contrast andlight-resistance and thus highly useful in a display element suitablefor a medium to large-scale display and as a liquid crystal compositiontherefor.

We claim:
 1. A liquid crystal composition comprising at least onecompound represented by each of the following general formulae I, II andIII: ##STR33## wherein R¹ to R³ represent each a hydrogen atom, analkyl, an optionally substituted cycloalkyl, an alkoxyalkyl or an alkoxygroup or a halogen atom; and A represents a ##STR34## group; ##STR35##wherein R⁴ and R⁵ represent each a hydrogen atom, an alkyl, anoptionally substituted cycloalkyl, an alkoxyalkyl or an alkoxy group ora halogen atom; and ##STR36## wherein R⁶ represents a hydrogen atom, analkyl, an optionally substituted cycloalkyl, an alkoxyalkyl or an alkoxygroup or a halogen atom; and R⁷ represents a hydrogen atom or a##STR37## group wherein R⁸ represents a hydrogen atom, an alkyl, anoptionally substituted cycloalkyl, an alkoxyalkyl or an alkoxy group ora halogen atom.
 2. A liquid crystal composition as claimed in claim 1,wherein said dye represented by the general formula I is at least onedye selected from among those of the general formula I wherein R¹ and R³represent each a hydrogen atom or an alkyl group;R² represents ahydrogen atom; and A represents a ##STR38## group.
 3. A liquid crystalcomposition as claimed in claim 1, wherein said dye represented by thegeneral formula I is at least one dye selected from among those of thegeneral formula I wherein R¹ and R³ represent each a hydrogen atom or analkyl group having 1 to 8 carbon atoms; R² represents a hydrogen atom;and A represents a ##STR39## group.
 4. A liquid crystal composition asclaimed in claim 1, wherein said dye represented by the general formulaI is at least one dye selected from among those of the general formula Iwherein R¹ represents a hydrogen atom or an alkyl group having 1 to 8carbon atoms;R² represents a hydrogen atom; R³ represents an alkyl grouphaving 1 to 8 carbon atoms; and A represents a ##STR40## group.
 5. Aliquid crystal composition as claimed in claim 1, wherein said dyerepresented by the general formula I is at least one dye selected fromamong those Of the general formula I wherein R¹ and R² represents each ahydrogen atom;R³ represents an alkyl group having 1 to 8 carbon atoms;and A represents a ##STR41## group.
 6. A liquid crystal composition asclaimed in claim 1, wherein said dye represented by the general formulaI is at least one dye selected from among those of the general formulaII wherein R⁴ and R⁵ represent each a hydrogen atom or an alkyl group.7. A liquid crystal composition as claimed in claim 1, wherein said dyerepresented by the general formula II is at least one dye selected fromamong those of the general formula II wherein R⁴ and R⁵ represent eachan alkyl group having 2 to 8 carbon atoms.
 8. A liquid crystalcomposition as claimed in claim 1, wherein said dye represented by thegeneral formula III is at least one dye selected from among those of thegeneral formula III wherein R⁶ represents a hydrogen atom or an alkylgroup;R⁷ represents a hydrogen atom or a ##STR42## group; and R⁸represents a hydrogen atom or an alkyl group.
 9. A liquid crystalcomposition as claimed in claim 1, wherein said dye represented by thegeneral formula III is at least one dye selected from among those of thegeneral formula III wherein R⁶ represents an alkyl group having 2 to 10carbon atoms;R⁷ represents a hydrogen atom or a ##STR43## group; and R⁸represents an alkyl group having 2 to 8 carbon atoms.
 10. A liquidcrystal composition as claimed in claim 1, which comprises at least onedye selected from among those of general formula I wherein R¹ and R³represent each a hydrogen atom or an alkyl group;R² represent a hydrogenatom; and A represents a ##STR44## group, as said dye represented by thegeneral formula I; at least one dye selected from among those of thegeneral formula II wherein R⁴ and R⁵ represent each a hydrogen atom oran alkyl group, as said dye represented by the general formula II; andat least one dye selected from among those of the general formula IIIwherein R⁶ represents a hydrogen atom or an alkyl group; R⁷ represents ahydrogen atom or a ##STR45## group; and R⁸ represents a hydrogen atom oran alkyl group; as said dye represented by the general formula III. 11.A liquid crystal composition as claimed in claim 1, which comprises atleast one dye selected from among those of general formula I wherein R¹and R³ represent each a hydrogen atom or an alkyl group having 1 to 8carbon atoms;R² represent a hydrogen atom; and A represents a ##STR46##group; as said dye represented by the general formula I; at least onedye selected from among those of the general formula II wherein R⁴ andR⁵ represent each an alkyl group having 2 to 8 carbon atoms, as said dyerepresented by the general formula II; and at least one dye selectedfrom among those of the general formula III wherein R⁶ represents analkyl group having 2 to 10 carbon atoms; R⁷ represents a hydrogen atomor a ##STR47## group; and R⁸ represents an alkyl group having 2 to 8carbon atoms; as said dye represented by the general formula III.
 12. Aliquid crystal composition as claimed in claim 1, which comprises atleast one dye selected from among those of general formula I wherein R¹represents a hydrogen atom or an alkyl group having 1 to 8 carbonatoms;R² represent a hydrogen atom; R³ represents an alkyl group having1 to 8 carbon atoms; and A represents a ##STR48## group; as said dyerepresented by the general formula I; at least one dye selected fromamong those of the general formula II wherein R⁴ and R⁵ represent eachan alkyl group having 2 to 8 carbon atoms, as said dye represented bythe general formula II; and at least one dye selected from among thoseof the general formula III wherein R⁶ represents an alkyl group having 2to 10 carbon atoms; R⁷ represents a hydrogen atom or a ##STR49## group;and R⁸ represents an alkyl group having 2 to 8 carbon atoms; as said dyerepresented by the general formula III.
 13. A liquid crystal compositionas claimed in claim 1, which comprises two or more dyes selected fromthose represented by the general formula III.
 14. A liquid crystalcomposition as claimed in claim 13, wherein at least one dye of thegeneral formula I wherein R⁷ is a hydrogen atom is employed togetherwith at least one dye of the general formula I wherein R⁷ is a ##STR50##group.
 15. A liquid crystal composition as claimed in claim 1, wherein anematic liquid crystal mixture comprising phenylcyclohexane liquidcrystal compound(s) as the major component is used as said liquidcrystal material.
 16. A display element comprising a liquid crystalcomposition charged between electrode bases at least one of which is atransparent, wherein said liquid crystal composition comprises at leastone compound represented by each of the following general formulae I, IIand III: ##STR51## wherein R¹ to R³ represent each a hydrogen atom, analkyl, an optionally substituted cycloalkyl, an alkoxyalkyl or an alkoxygroup or a halogen atom; and A represents a ##STR52## group; ##STR53##wherein R⁴ and R⁵ represent each a hydrogen atom, an alkyl, anoptionally substituted cycloalkyl, an alkoxyalkyl or an alkoxy group ora halogen atom; and ##STR54## wherein R⁶ represents a hydrogen atom, analkyl, an optionally substituted cycloalkyl, an alkoxyalkyl or an alkoxygroup or a halogen atom; and R⁷ represents a hydrogen atom or a##STR55## group wherein R⁸ represents a hydrogen atom, an alkyl, anoptionally substituted cycloalkyl, an alkoxyalkyl or an alkoxy group ora halogen atom.
 17. A display element as claimed in claim 16, wherein aliquid crystal composition which comprises at least one dye selectedfrom among those of general formula I wherein R¹ and R³ represent each ahydrogen atom or an alkyl group;R² represent a hydrogen atom; and Arepresents a ##STR56## group, as said dye represented by the generalformula I; at least one dye selected from among those of the generalformula II wherein R⁴ and R⁵ represent each a hydrogen atom or an alkylgroup, as said dye represented by the general formula II; and at leastone dye selected from among those of the general formula III wherein R⁶represents a hydrogen atom or an alkyl group; R⁷ represents a hydrogenatom or a ##STR57## group; and R⁸ represents a hydrogen atom or an alkylgroup, as said dye represented by the general formula III; is used. 18.A display element as claimed in claim 16, wherein a liquid crystalcomposition as claimed in claim 16 which comprises at least one dyeselected from among those of general formula I wherein R¹ represents ahydrogen atom or an alkyl group having 1 to 8 carbon atoms;R² representa hydrogen atom; R³ represents an alkyl group having 1 to 8 carbonatoms; and A represents a ##STR58## group, as said dye represented bythe general formula I; at least one dye selected from among those of thegeneral formula II wherein R⁴ and R⁵ represent each an alkyl grouphaving 2 to 8 carbon atoms, as said dye represented by the generalformula II; and at least one dye selected from among those of thegeneral formula III wherein R⁶ represents an alkyl group having 2 to 10carbon atoms; R⁷ represents a hydrogen atom or a ##STR59## group; and R⁸represents an alkyl group having 2 to 8 carbon atoms; as said dyerepresented by the general formula III; is used.
 19. A display elementas claimed in claim 16, wherein said liquid crystal material is anematic liquid crystal mixture comprising phenylcyclohexane liquidcrystal compound(s) as the major component.